The present invention relates to a semiconductor device having a copper wiring and its fabrication method.
As a semiconductor device is more highly integrated, the width of a wiring and the interval between wirings are decreased and resultantly the resistance of a wiring or the capacitance between wirings is increased. When the resistance or capacity increases, the speed for an electrical signal to pass through a wiring lowers and resultantly the operation speed of a semiconductor device is limited. To prevent the above phenomenon, a method for forming a low-resistance wiring by using a copper (Cu) film has been positively studied in recent years.
A conventional semiconductor device, specifically a semiconductor device having a wiring formed by a Cu film and its fabrication method are described below by referring to the accompanying drawings.
FIGS. 21 to 26 are sectional views showing steps of a conventional semiconductor-device fabrication method.
First, as-shown in FIG. 21, a first silicon-dioxide (SiO2) film 3, a silicon nitride (Si3N4) film 4, and a second SiO2 film 5 are formed in order on a semiconductor substrate 1 provided with a lower-layer wiring 2 formed by a Cu film.
Then, as shown in FIG. 22, a via hole 6 reaching the lower-layer wiring 2 is formed on the first SiO2 film 3 and the Si3N4 film 4 and a wiring groove 7 connecting with the via hole 6 is formed on the second SiO2 film 5 by alternately applying the lithography method and the dry etching method twice each. In this case, a Cu film constituting the lower-layer wiring 2 is exposed to the bottom of the via hole 6 while the surface of the Cu film is immediately oxidized by oxygen (O2) in the air. Thereby, copper oxide {CuOx(x greater than O)} layer 8 is formed on the portion of the lower-layer wiring 2 exposed to the via hole 6.
Then, as shown in FIG. 23, the CuOx layer 8 and a part of a Cu film forming lower-layer wiring 2 is removed by the sputter-etching method using an inert gas. However, because the removed portion is small compared to the entire lower-layer wiring 2, the removed portion is omitted from FIG. 23 downward.
Then, as shown in FIG. 24, a titanium nitride (TiN) film 9 is formed on the second SiO2 film 5 including insides of the via hole 6 and wiring groove 7 by the chemical vapor deposition method. Thereby, the TiN film 9 is formed on the portion of the lower-layer wiring 2 exposed to the via hole 6 (that is, on the bottom face of the via hole 6), the wall surface of the via hole 6, and the wall surface and bottom face of the wiring groove 7 respectively.
Then, as shown in FIG. 25, a first Cu film 10 is formed on the TiN film 9 by the physical vapor deposition method and then, a second Cu film 11 is formed on the first Cu film 10 by the plating method to embed the via hole 6 and the wiring groove 7 by the second Cu film 11.
Finally, as shown in FIG. 26, the portions of the TiN film 9, first Cu film 10, and second Cu film 11 outside the wiring groove 7 are removed by the chemical-mechanical polishing method (CMP method). Thereby, an upper-layer wiring 12 is formed which is constituted by the TiN film 9, first Cu film 10, and second Cu film 11 embedded in the via hole 6 and wiring groove 7.
In the case of the conventional semiconductor device shown in FIG. 26, the TiN film 9 functions as a barrier metal film for preventing diffusion of Cu atoms contained in the first Cu film 10 and second Cu film 11.
However, the above-described prior art has the following problems.
FIGS. 27 to 30 are illustrations for explaining problems of the prior art. In FIGS. 27 to 30, members same as those of the conventional semiconductor device shown in FIGS. 21 to 26 are provided with the same symbols and their description is omitted.
As shown in FIG. 27, the first problem of the prior art is that when operating a semiconductor device for a long time at a high temperature, the portion of the TiN film 9 nearby the lower-layer wiring 2 is oxidized and thereby, a high-resistance titanium oxide (TiO2) layer 13 is formed. When the TiO2 layer 13 is formed, the connection resistance between the lower-layer wiring 2 and the upper-layer wiring 12 increases and thereby, the operation speed of the semiconductor device lowers. This phenomenon specifically occurs due to the following mechanism. That is, to form the via hole 6 or wiring groove 7 by the dry etching method, oxygen (O) atoms contained in the first SiO2 film 3 or second SiO2 film 5 are implanted into a Cu film constituting the lower-layer wiring 2 and resultantly, an oxygen-atom-containing layer 14 is formed in the lower-layer wiring 2. The oxygen-atom-containing layer 14 is distributed in a range wider than the CuOx layer 8 shown in FIG. 22. When operating a semiconductor device for a long time under the above state, oxygen atoms contained in the oxygen-atom-containing layer 14 move toward the upper-layer 12 and resultantly, the portion of the TiN film 9 nearby the lower-layer wiring 2 is oxidized and the TiO2 layer 13 is formed.
Then, as shown in FIG. 28, the second problem of the prior art is that Cu atoms pass through the TiN film 9 and reaches the first SiO2 film 3 and second SiO2 film 5 when using a semiconductor device for a long time at a high temperature because the power for preventing diffusion of Cu atoms contained in the first Cu film 10 and second Cu film 11 by the TiN film 9 is not sufficient (arrow in FIG. 28 shows diffusion direction of Cu atoms). Cu atoms reaching the first SiO2 film 3 and second SiO2 film 5 form mobile ions in the first SiO2 film 3 and second SiO2 film 5 and thereby, leak current increases between adjacent vias or wirings (that is upper-layer wiring 12) and resultantly the semiconductor device malfunctions.
Then, the third problem of the prior art is that when removing the CuOx film 8 and a part of a Cu film constituting lower-layer wiring 2 by the sputter-etching method using an inert gas (refer to FIG. 23), Cu atoms contained in the lower-layer wiring 2 are scattered and attach to the wall surface of the via hole 6 or wiring groove 7 and thereby, a Cu layer 15 is formed as shown in FIG. 29. When the Cu layer 15 is formed on the wall surface of the via hole 6 or wiring groove 7, many Cu atoms are diffused in the first SiO2 film 3 and second SiO2 film 5 and thereby, adjacent vias or wirings are unexpectedly electrically connected each other and resultantly the yield of semiconductor devices is extremely lowered.
Finally, the fourth problem of the prior art is that when removing the portions of the TiN film 9, first Cu film 10, and second Cu film 11 outside the wiring groove 7 by the CMP method (refer to FIGS. 25 and 26), exfoliation (refer to the portion enclosed by the broken line in FIG. 30) occurs at the interface between the second SiO2 film 5 and the TiN film 9, as shown in FIG. 30. When the TiN film 9 is exfoliated from the second SiO2 film 5, the first Cu film 10 and second Cu film 11 are also exfoliated from the second SiO2 film 5 with moving of the polishing cloth and thereby, a laminated wiring structure formed on a semiconductor substrate 1 is broken and resultantly the yield of semiconductor devices is extremely lowered.
In view of the above mentioned, it is an object of the present invention to make it possible to prevent a semiconductor device from malfunctioning and fabricate semiconductor devices at a high yield, while embodying a wiring with low-resistance employing a Cu film.
To achieve the above object, a first semiconductor device of the present invention comprises a lower-layer wiring made of copper or a copper alloy and formed on a semiconductor substrate, an insulating film deposited on the lower-layer wiring and provided with a via hole reaching the lower-layer wiring, and a metal film deposited in the via hole, wherein the portion of the lower-layer wiring contacting with the metal film is a copper-silicide layer.
According to the first semiconductor device, because the portion of the lower-layer wiring contacting with the metal film in the via hole is the copper-silicide layer, it is possible to prevent oxygen atoms which implanted into a copper film or a copper-alloy film (these are respectively hereafter referred to as a copper film) constituting the lower-layer wiring under the dry etching for forming the via hole, from reaching the metal film in the via hole. Therefore, a high-resistance oxidation layer is not formed in the portion of metal film contacting with the lower-layer wiring. Therefore, even when operating the semiconductor device for a long time at a high temperature, it is possible to avoid that the connection resistance between the lower-layer wiring and the upper-layer wiring from increasing and thereby, prevent the operation speed of the semiconductor device from lowering. That is, according to the first semiconductor device, it is possible to solve the first problem of the prior art.
In the case of the first semiconductor device, it is preferable that the thickness of the copper-silicide layer ranges between 0.5 nm and 20 nm (both included).
Thus, it is possible to securely prevent oxygen atoms in the copper film constituting the lower-layer wiring from reaching the metal film in the via hole and moreover prevent the connection resistance between the lower-layer wiring and the upper-layer wiring from being excessively increased by the fact that the copper-silicide layer is excessively thickened.
In the case of the first semiconductor device, it is preferable that the metal film is a titanium-nitride film.
Thus, by using the titanium-nitride film as a barrier film and forming an upper-layer wiring made of a copper film, it is possible to prevent copper atoms contained in the copper film from diffusing.
A second semiconductor device of the present invention comprises an insulating film deposited on a semiconductor substrate and provided with a concave portion, and a wiring metal film embedded in the concave portion and made of copper or a copper alloy, in which a titanium-nitride-silicide layer and a titanium-nitride film are formed in order from the insulating-film side between the insulating film and the wiring metal film.
According to the second semiconductor device, a titanium-nitride-silicide layer and a titanium-nitride film are formed between an insulating film and a wiring copper film embedded in a concave portion formed in the insulating film. In this case, the laminated structure of the titanium-nitride-silicide layer and the titanium-nitride film has the power for preventing diffusion of copper atoms higher than that of a single-layer structure of only the titanium-nitride film or a single-layer structure of only the titanium-nitride-silicide layer. Therefore, because copper atoms contained in the wiring copper film do not easily reach the insulating film, the concentration of copper atoms in the insulating film lowers. Therefore, even when operating the semiconductor device for a long time at a high temperature, it is possible to avoid a leak current between adjacent vias or wirings from increasing and thereby, prevent the semiconductor device from malfunctioning. That is, according to the second semiconductor device, it is possible to solve the second problem of the prior art.
In the case of the second semiconductor device, it is preferable that the thickness of the titanium-silicide layer ranges between 0.5 nm and 10 nm (both included).
Thus, the power for preventing copper atoms from diffusing is securely improved and it is possible to prevent the resistance of a via or wiring from being excessively increased by the fact that the titanium-nitride-silicide layer is excessively thickened.
In the case of the second semiconductor device, it is preferable that the thickness of the titanium-nitride film ranges between 0.5 nm and 10 nm (both included).
Thus, the power for preventing copper atoms from diffusing is securely improved and it is possible to prevent the resistance of a via or wiring from being excessively increased by the fact that the titanium-nitride film is excessively thickened.
A third semiconductor device of the present invention comprises an insulating film deposited on a semiconductor substrate and provided with a concave portion, and a wiring metal film embedded in the concave portion and made of copper or a copper alloy, in which a metal film, a titanium-nitride-silicide layer, and a titanium-nitride film are formed in order from the insulating-film side between the insulating film and the wiring metal film.
According to the third semiconductor device, a metal film, a titanium-nitride-silicide layer, and a titanium-nitride film are formed between an insulating film and a wiring copper film embedded in a concave portion formed in the insulating film. In this case, when using a titanium-nitride film as the metal film, the laminated structure of a titanium-nitride film, a titanium-nitride-silicide layer, and a titanium-nitride film has the power for preventing copper atoms from diffusing higher than that of the laminated structure of a titanium-nitride-silicide layer and a titanium-nitride layer. Therefore, because it is more difficult for copper atoms contained in a wiring copper film to reach an insulating film in comparison with the case of the second semiconductor device of the present invention, the concentration of copper atoms in the insulating film is further lowered. Therefore, even when operating a semiconductor device for a long time at a high temperature, it is possible to securely avoid a leak current between adjacent vias or wirings from increasing and thereby securely prevent the semiconductor device from malfunctioning. That is, according to the third semiconductor device, it is possible to solve the second problem of the prior art.
In the case of the third semiconductor device, it is preferable that the metal film is another titanium-nitride film.
Thus, the power for preventing copper atoms from diffusing is securely improved.
In the case of the third semiconductor device, it is preferable the thickness of the titanium-nitride-silicide layer ranges between 0.5 nm and 10 nm (both included).
Thus, the power for preventing copper atoms from diffusing is securely improved and it is possible to prevent the resistance of a via or wiring from being excessively increased by the fact that the titanium-nitride-silicide layer is excessively thickened.
In the case of the third semiconductor device, it is preferable the thickness of the titanium-nitride film ranges between 0.5 nm and 10 nm (both included).
Thus, the power for preventing copper atoms from diffusing is securely improved and it is possible to prevent the resistance of a via or wiring from being excessively increased by the fact that the titanium-nitride film is excessively thickened.
A first semiconductor-device fabrication method of the present invention comprises a step of forming a lower-layer wiring made of copper or a copper alloy on a semiconductor substrate, a step of forming an insulating film having a via hole reaching the lower-layer wiring on the lower-layer wiring, a step of forming a copper-silicide layer on the portion of the lower-layer wiring exposed to the via hole, and a step of depositing a metal film on the copper silicide layer in the via hole.
According to the first semiconductor-device fabrication method, an insulating film having a via hole is formed on a lower-layer wiring formed by a copper film and then, a copper silicide layer is formed on the portion of the lower-layer wiring exposed to the via hole, and then a metal film is deposited in the via hole. Therefore, because the first semiconductor device of the present invention can be fabricated, it is possible to solve the first problem of the prior art.
Moreover, according to the first semiconductor-device fabrication method, by forming a copper silicide layer in the portion of a lower-layer wiring exposed to a via hole, it is possible to remove a copper oxide layer formed in the portion when forming the via hole. In other words, the bottom of the via hole can be cleaned by a chemical method referred to as copper-silicide formation instead of the conventional sputter etching method. Therefore, it is possible to avoid that copper atoms contained in the lower-layer wiring are scattered and attach to the wall surface of the via hole and then reach the insulating film. Therefore, because adjacent vias are not unexpectedly electrically connected each other, it is possible to prevent the yield of semiconductor devices from lowering. That is, according to the first semiconductor-device fabrication method, it is possible to solve the third problem of the prior art.
In the case of the first semiconductor-device fabrication method, it is preferable that the step of forming the copper silicide layer includes a step of exposing the portion of the lower-layer wiring exposed to the via hole to silane.
Thus, it is possible to securely form a copper silicide layer.
When forming a copper silicide layer by using silane, it is preferable that the step of exposing the portion to the silane includes a step of setting the temperature for heating the semiconductor substrate to 350xc2x0 C. or higher and moreover setting the product of the partial pressure of the silane and the time for exposing the portion to the silane to about 6.65xc3x9710 Paxc2x7sec or less.
Thus, it is possible to set the thickness of the copper silicide layer to a value between 0.5 nm and 20 nm (both included). As a result, it is possible to securely prevent oxygen atoms in a copper film constituting the lower-layer wiring from reaching the metal film in the via hole and moreover prevent the connection resistance between the lower-layer wiring and the upper-layer wiring from being excessively increased by the fact that the copper silicide layer is excessively thickened.
When forming a copper silicide layer by using silane, it is preferable that the step of exposing the portion to the silane includes a step of setting the temperature for heating the semiconductor substrate to 350xc2x0 C. or lower and moveover setting the product of the partial pressure of the silane and the time for exposing the portion to the silane to a value between about 6.65xc3x9710xe2x88x922 and 3.33xc3x97102 Paxc2x7sec (both included).
Thus, it is possible to set the thickness of the copper silicide layer to a value between 0.5 nm and 20 nm (both included). As a result, it is possible to securely prevent oxygen atoms in a copper film constituting the lower-layer wiring from reaching the metal film in the via hole and moreover prevent the connection resistance between the lower-layer wiring and the upper-layer wiring from being excessively increased by the fact that the copper silicide layer is excessively thickened.
When forming a copper silicide layer by using silane, it is preferable that the step of forming the copper silicide layer further includes a step of heating the semiconductor substrate at a reduced pressure before the step of exposing the portion to the silane.
Thus, it is possible to decompose a copper oxide layer formed in the portion of the lower-layer wiring exposed to the via hole before forming the copper silicide layer, in other words, it is possible to clean the surface of a copper film constituting the lower-layer wiring before forming the copper silicide layer, it is possible to accelerate uniform formation of the copper silicide layer. Moreover, in this case, it is preferable that the step of heating the semiconductor substrate includes a step of setting the partial pressure of oxygen to about 1.33xc3x9710xe2x88x924 Pa or lower and setting the temperature and the time for heating the semiconductor substrate to about 300xc2x0 C. or higher and about 3 sec or more. Thus, it is possible to securely clean the surface of the copper film constituting the lower-layer wiring.
A second semiconductor-device fabrication method of the present invention comprises a step of forming an insulating film having a concave portion on a semiconductor substrate, a step of depositing a silicon layer and a titanium nitride film in order on the insulating film so that the concave portion is embedded up to the middle of it, and a step of depositing a wiring metal film made of copper or a copper alloy on the titanium nitride film so that the concave portion is completely embedded, in which the titanium nitride film is deposited by the chemical vapor deposition method using a compound containing titanium.
According to the second semiconductor-device fabrication method, a silicon layer and a titanium nitride film are deposited in order on an insulating film having a concave portion so that the concave portion is embedded up to the middle of it and then, a wiring metal film made of copper or a copper alloy is deposited so that the concave portion is completely embedded. In this case, because the titanium nitride film is deposited on the silicon layer by the chemical vapor deposition method using the compound containing titanium, silicon atoms in the silicon layer react with the compound containing titanium and thereby a titanium-nitride-silicide layer is formed. Therefore, because the second semiconductor device of the present invention can be fabricated, it is possible to solve the second problem of the prior art.
Moreover, according to the second semiconductor-device fabrication method, because a silicon layer and a titanium-nitride-silicide layer is present between an insulating film and a titanium nitride film, when the insulating film is a SiO2 film or the like, the adhesiveness between the insulating film and the titanium nitride film is improved compared to the case in which the insulating film directly contacts with the titanium nitride film. Therefore, when forming a via or wiring by removing the portions of the titanium nitride film and the wiring metal film outside the concave portion by, for example, the chemical-mechanical polishing method, it is possible to avoid that exfoliation occurs at the interface between the insulating film and the titanium nitride film, that is, a laminated wiring structure on the semiconductor substrate is broken and thereby, it is possible to prevent the yield of semiconductor devices from lowering. That is, according to the second semiconductor-device fabrication method, it is possible to solve the fourth problem of the prior art.
In the case of the second semiconductor-device fabrication method, it is preferable that the silicon layer is deposited by exposing the surface of the insulating film including the inside of the concave portion to silane.
Thus, it is possible to securely deposit the silicon layer. Moreover, in this case, when exposing the surface to the silane, it is preferable to set the temperature for heating the semiconductor substrate to 350xc2x0 C. or higher and to set the product of the partial pressure of the silane and the time for exposing the surface to the silane to about 1.33xc3x9710xe2x88x922 Paxc2x7sec or more. Thus, it is possible to form a silicon layer for forming a titanium-nitride-silicide layer having a thickness large enough to prevent diffusion of copper atoms.
A third semiconductor-device fabrication method of the present invention comprises a step of forming an insulating film having a concave portion on a semiconductor substrate, a step of depositing a metal film, a silicon layer, and a titanium nitride film in order on the insulating film so that the concave portion is embedded up to the middle of it, and a step of depositing a wiring metal film made of copper or a copper alloy on the titanium nitride film so that the concave portion is completely embedded, in which the titanium nitride film is deposited by the chemical vapor deposition method using a compound containing titanium.
According to the third semiconductor-device fabrication method, a metal film, a silicon layer, and a titanium nitride are deposited in order on an insulating film having a concave portion so that the concave portion is embedded up to the middle of it and then, a wiring metal film made of copper or a copper alloy is deposited so that the concave portion is completely embedded. In this case, because the titanium nitride film is deposited on the silicon layer by the chemical vapor deposition method using the compound containing titanium, silicon atoms in the silicon layer reacts with the compound containing titanium and thereby, a titanium-nitride-silicide layer is formed. Therefore, because a third semiconductor device of the present invention can be fabricated, it is possible to solve the second problem of the prior art.
Moreover, according to the third semiconductor-device fabrication method, because a silicon layer is deposited on an insulating film with a metal film interposed between the silicon layer and the insulating film, the insulating film does not directly contact with the silicon layer even if the insulating film is an insulating film of a specific type having an inferior adhesiveness with the silicon layer such as an SiOF film. Therefore, when removing the portions of the titanium nitride film and the wiring metal film outside the concave portion by, for example, the chemical-mechanical polishing method and thereby forming a via or wiring, it is possible to avoid that a laminated wiring structure on the semiconductor substrate is broken and thereby prevent the yield of semiconductor devices from lowering. That is, according to the third semiconductor-device fabrication method, it is possible to solve the fourth problem of the prior art.
In the case of the third semiconductor-device fabrication method, it is preferable that the metal film is another titanium nitride film.
Thus, the power for preventing diffusion of copper atoms is securely improved.
In the case of the third semiconductor-device fabrication method, it is preferable that the silicon layer is deposited by exposing the surface of the metal film including the inside of the concave portion to silane.
Thus, it is possible to securely deposit the silicon layer. Moreover, in this case, to expose the surface to the silane, it is preferable to set the temperature for heating the semiconductor substrate to 350xc2x0 C. or higher and the product of the partial pressure of the silane and the time for exposing the surface to the silane to about 1.33xc3x9710xe2x88x922 Paxc2x7sec or more. Thus, it is possible to form a silicon layer for forming a titanium-nitride-silicide layer having a thickness large enough to prevent diffusion of copper atoms.